GB2367355A

GB2367355A - A heat exchanger for exhaust gas of an ic engine

Info

Publication number: GB2367355A
Application number: GB0117752A
Authority: GB
Inventors: Gerd Tiefenbacher
Original assignee: DaimlerChrysler AG
Current assignee: Daimler AG
Priority date: 2000-07-22
Filing date: 2001-07-20
Publication date: 2002-04-03
Anticipated expiration: 2021-07-20
Also published as: GB0117752D0; FR2812027B1; GB2367355B; FR2812027A1; DE10035760A1

Abstract

A heat exchanger for exhaust gas of an internal combustion engine comprises a cooling chamber 4 around which coolant flows, a cooling chamber inlet 3 and a cooling chamber outlet 5, and the flow of exhaust gas is controlled by means of a closure device 2, which performs a relative motion into a closing or flow position owing to thermal expansion. An exhaust pipe 7 with the closure device 2 may be provided in the coolant chamber 4. The heat exchanger may have an exhaust pipe 7 with control openings 6 arranged on the circumference within the cooling chamber, exposing the cooling-chamber inlet 3 and outlet 5 by means of thermal expansion. In addition to the exhaust pipe 7, the cooling chamber may accommodate a further control pipe 15, which is arranged in an axially displaceable manner co-axially or in contact with the exhaust pipe 7 and contains cooling chamber openings 3, 5 corresponding to the control openings 6 of the exhaust pipe 7. The control openings 6 may be closed by a closure device 2 made from a bimetallic material. The exhaust pipe 7 may have baffles 12 and a venturi nozzle 16 in order to control the exhaust flow. The heat exchanger may have more than one cooling chamber 4.

Description

1 2367355 A heat exchange The invention relates to a heat exchanger for

exhaust gas of an internal combustion engine.

To limit the temperature-related ageing of catalytic converters, measures to limit the gas inlet temperature to a permissible maximum are required, for example, with an NOx storage converter for a direct-injection sparkignition engine. Corresponding measures in terms of the configuration of the engine or combustion lead to increased pollutant emissions and increased fuel consumption or reduce the rated power of the engine. Active elements in exhaust system engineering, such as switched bypass or heat exchanger systems, require a technically high-quality and correspondingly expensive shutoff member, such as an exhaust flap, a valve or other actively moved control elements in the exhaust line. Moreover, mechanical or electronic control is required and this represents a considerable outlay when the control unit and additional components are included.

DE 197 46 658 Al has already disclosed the use of a heat exchanger of this kind. This is an exhaust catalytic-converter system for controlling the temperature range of an NOx storage device for treating a flow of exhaust gas coming from an internal combustion engine and carried in an exhaust line. A first catalytic converter and NOx storage device are provided in at least one exhaust line in each case, at least one heat exchanger being arranged in the exhaust line. This is designed as a countercurrent heat exchanger, through which coolant flows in a sleeve formed by a double wall. Water or air is provided as the coolant and flows through the heat exchanger as a forced flow. The heat exchanger is thus embodied as a separate heat exchanger based on the forced countercurrent principle. On the one hand, a heat exchanger of this kind requires a considerable amount of installation space and must be supplied with corresponding control elements and control electronics.

The present invention seeks to design and arrange a heat exchanger for exhaust gas in such a way that a minimum amount of installation space and no control elements or control electronics are required.

According to the present invention there is provided a heat exchanger for exhaust gas of an internal combustion engine with at least one closure device, the heat exchanger having a cooling chamber, around which coolant flows, a cooling-chamber inlet and a cooling-chamber outlet, wherein the flow of exhaust gas is controlled by means of a closure device, which performs a relative motion into a closing or flow position owing to thermal expansion.

This ensures that the flow of exhaust gas is controlled without expensive detection and control systems. The increase in the temperature of the heat exchanger thus formed and of the closure device brings about the cooling effect. In a corresponding way, cooling of the closure device leads to closure of the heat exchanger. It is advantageous for this purpose that an exhaust pipe with the closure device controlled by thermal expansion is provided in the coolant chamber and the exhaust pipe has control openings arranged on the circumference, which expose the cooling-chamber inlet and the cooling-chamber outlet by means of thermal expansion. For this purpose, the exhaust pipe is attached within the coolant chamber at only one end, with the result that heating leads to unilateral axial expansion of the pipe. This expansion of the pipe is associated with an axial offset of the control openings provided in the pipe, with the result that they expose the cooling chamber or cooling- chamber openings.

It is furthermore advantageous that a cooling-chamber wall is arranged coaxially with the exhaust pipe and sections of the cooling-chamber wall rest against the exhaust pipe or are in effective connection with the exhaust pipe and that the control opening is arranged in such a way that an axial offset occurs between the control opening and the cooling chamber or a cooling-chamber opening if there is an increase in the temperature of the exhaust pipe. The cooling-chamber wall thus formed or that part of the coolingchamber wall that rests against the exhaust pipe closes the control openings in the cold condition. In the hot condition, an axial offset of the exhaust pipe occurs within the cooling-chamber wall, and that part of the cooling-chamber wall that is in contact exposes the control openings.

For this purpose, it is advantageous that a cooling-chamber wall of the cooling chamber is connected at the inlet end and the outlet end to a manifold or to an exhaust system, and the exhaust pipe is connected to the manifold or the exhaust system only at the outlet end or the inlet end. This ensures axial expansion of the exhaust pipe within the cooling chamber or relative to the cooling chamber.

Finally, according to a preferred embodiment of the invention provision is made for different cooling chambers to have a common transfer passage, which forms a return flow opening at the end of the heat exchanger, and for them to be connected by this passage. The exhaust gas to be cooled can thus enter the cooling chamber through the exposed cooling-chamber openings and flow back into the exhaust system via the return flow opening at the end of the heat exchanger.

it is particularly advantageous if, on the inside, the exhaust pipe has an inflow aid such as a baffle in the region of the control opening and an outflow aid in the region of the control opening. This ensures that the exhaust gas to be cooled or some of it flows into the cooling chamber and back out of this into the exhaust section more quickly and more easily.

In the context of the design and arrangement according to the invention, it is particularly advantageous if in addition to the exhaust pipe, the cooling chamber accommodates a further control pipe, which is arranged in an axially displaceable manner coaxially or in contact with the exhaust pipe and contains the cooling-chamber openings corresponding to the control openings of the exhaust pipe. The control pipe replaces the contacting parts of the cooling-chamber wall with the particular advantage that coolingchamber inlets and cooling-chamber outlets can be formed without forming the transfer passage. The two pipes expand axially in opposite directions and thus form the closure device according to the invention.

It is advantageous for this purpose that the exhaust pipe is connected to the manifold at the inlet end or the outlet end, and the control pipe is connected to it inversely at the outlet end or the inlet end, and the thermal expansion of the two pipes takes place in opposite directions. The inverse attachment of the pipes has the advantage that the lengthening of the pipes owing to the thermal expansion is complementary or combined, making it possible to achieve significantly larger cooling- chamber openings.

It is furthennore advantageous that an exhaust pipe fitted with a venturi nozzle and having control openings arranged on the circumference upstream and downstream of the venturi nozzle is arranged within or coaxially with respect to a control pipe, the control pipe having cooling-chamber openings on the circumference in the region of the control openings of the exhaust pipe, and both pipes being arranged in such a way that they can move axially relative to one another owing to the thermal expansion.

It is ftirthermore advantageous that the material of the exhaust pipe has a different coefficient of thermal expansion from the material of the cooling chamber or of the control pipe or that the control opening is closed by a closure device made from bimetallic material. The choice of different materials favours thermal expansion and the cross section to be opened of the cooling-chamber openings.

It is also advantageous that, together with the control pipe, the coolingchamber wall forms the cooling chamber adapted to the external space conditions on the vehicle floor and that a mixing section is provided between the cooling chamber and a catalytic converter. The operating capability of the heat exchanger is thus ensured within the given space conditions in an engine compartment or on the underside of a motor vehicle.

Further advantages and details of the invention are explained in the patent claims and in the following description and are illustrated in the figures, of which:

Figure I shows a basic diagram of a heat exchanger with a cooling chamber, an exhaust pipe and a control pipe, a cold operating condition being illustrated in the top half of the picture and a hot operating condition being illustrated in the bottom half of the picture, Figure 2 shows a sectional representation of a heat exchanger with two cooling chambers, a cold operating condition being illustrated in the top half of the picture and a hot operating condition being illustrated in the bottom half of the picture.

In Figure 1, a heat exchanger is indicated by 1. The heat exchanger I has a cooling chamber 4, which is formed by a cooling-chamber wall 9, an exhaust pipe 7 and a control pipe 15. The exhaust pipe 7 is arranged within the control pipe 15. Both pipes 7, 15 expand when heated. Owing to the fact that they are fixed at one end, an axial offset occurs between them.

According to Figure 1, the cooling chamber 4 is connected at its righthand and left-hand ends to respective schematically represented manifolds 8 by its cooling-chamber wall 9 and has a rectangular cross section. The manifold represents the part of the exhaust system between the combustionchamber outlet of the engine and the NOx catalytic converter or silencer.

The exhaust pipe 7 is arranged coaxially with respect to a centre line 18 of the cooling chamber 4 and at the right-hand end in Figure 1, i.e. at the exhaust inlet end or engine end, is connected directly to the manifold 8 with the cooling-chamber wall 9. In the central area, downstream of a cooling-chamber inlet 3, the exhaust pipe 7 has a taper 16 in the form of a venturi nozzle, with the result that the flow of exhaust gas entering from the right in Figure 1, i.e. at the exhaust inlet end or engine end, suffers a pressure loss within this flow section of the exhaust pipe 7. Upstream and downstream of the taper 16 or venturi nozzle, the exhaust pipe 7 has control openings 6 in its circumference, which are in effective connection with the control pipe 15 and the cooling-chamber openings 3, 5 provided therein. The exhaust pipe 7 and the control pipe 15 form a temperaturedependent axial offset relative to one another owing to thermal expansion, with the result that, in the cold condition, the control openings 6 and the cooling-chamber openings 3 are arranged offset relative to one another and, in the hot condition, they assume a condition in which they are almost congruent.

The control pipe 15 is likewise arranged coaxially with respect to the coolingchamber centre line 18 and the exhaust pipe 7 and, at the lefthand end in Figure 1, i.e. at the exhaust outlet end or converter end, is connected directly to the manifold 8 with the cooling-chamber wall 9. In the region of the connection points 17 and in the region of the control openings 6 of the exhaust pipe 7, the control pipe 15 has the coolingchamber openings 3, 5.

In the upper half of Figure 1, the control openings 6 and the coolingchamber openings 3, 5 are arranged in such a way that there is an axial offset between the control openings 6 and the cooling-chamber openings 3, 5 in the cold operating condition, i.e. up to about 300' C, and they are closed. The distance between the respectively corresponding centres of the openings is accordingly greater than or equal to the width of the coolingchamber openings 3, 5.

In the lower half of Figure 1, the control openings 6 and the coolingchamber openings 3, 5 are arranged one above the other in the hot operating condition, i.e. from about 400'C, owing to the thermal expansion of the exhaust pipe 7 and the control pipe 15 or the materials used for them, i.e. the offset between the respective centres of the openings is smaller or reduced to zero.

The exhaust gas flowing in from the right in Figure I is delayed by the subsequent venturi nozzle 16 arranged downstream of the cooling-chamber inlet 3, i.e. an increase in pressure occurs upstream of the venturi nozzle. This rise in pressure encourages part of the mass flow to branch off into the cooling chamber 4. The exhaust gas flowing into the cooling chamber 4 via the control opening 6 and the cooling-chamber opening 3 is delayed in the cooling chamber 4 owing to the increasing flow cross section and an increase in pressure occurs at this point. The exhaust gas is accordingly reaccelerated when it enters the exhaust pipe 7 since the two mass flows reunite there and the total flow cross section becomes smaller. An acceleration and hence a decrease in pressure occurs. With the assistance of the pressure difference thus produced within the cooling chamber 4, the exhaust gas flows through the open cooling-chamber inlet 3 into the cooling chamber 4 and, having been cooled, flows back into the exhaust pipe 7 through the coolingchamber outlet 5 at the end of the cooling chamber 4.

Claims

1. A heat exchanger for exhaust gas of an internal combustion engine with at least one closure device, the heat exchanger having a cooling chamber, around which coolant flows, a cooling-chamber inlet and a cooling-chamber outlet, wherein the flow of exhaust gas is controlled by means of a closure device, which performs a relative motion into a closing or flow position owing to thermal expansion.

2. A heat exchanger according to Claim 1, wherein an exhaust pipe with a closure device controlled by thermal expansion is provided in the coolant chamber.

3. A heat exchanger according to Claim I or 2, wherein an exhaust pipe with control openings arranged on the circumference is provided within the cooling chamber, exposing the cooling-chamber inlet and the coolingchamber outlet by means of thermal expansion.

4. A heat exchanger according to any one of the preceding claims, wherein a cooling-chamber wall is arranged coaxially with the exhaust pipe and sections of the cooling-chamber wall rest against the exhaust pipe or are in effective connection with the exhaust pipe.

5. A heat exchanger according to any one of the preceding claims, wherein the control opening is arranged in such a way that an axial offset occurs between the control opening and the cooling chamber or a cooling-chamber opening if there is an increase in the temperature of the exhaust pipe.

6. A heat exchanger according to any one of the preceding claims, wherein a cooling-chamber wall of the cooling chamber is connected at the inlet end and the outlet end to a manifold or to an exhaust system, and the exhaust pipe is connected to the manifold or the exhaust system only at the outlet end or the inlet end.

7. A heat exchanger according to any one of the preceding claims, wherein different cooling chambers have a common transfer passage, which forms a return flow opening at the end of the heat exchanger, and are connected by this passage.

S. A heat exchanger according to any one of the preceding claims, wherein, on the inside, the exhaust pipe has an inflow aid such as a baffle in the region of the control opening and an outflow aid such as a baffle in the region of the control opening.

9. A heat exchanger according to any one of the preceding claims, wherein, in addition to the exhaust pipe, the cooling chamber accommodates a further control pipe, which is arranged in an axially displaceable manner coaxially or in contact with the exhaust pipe and contains the coolingchamber openings corresponding to the control openings of the exhaust pipe.

10. A heat exchanger according to any one of the preceding claims, wherein the exhaust pipe is connected to the manifold at the inlet end or the outlet end, and the control pipe is connected to it inversely at the outlet end or the inlet end, and the thermal expansion of the two pipes takes place in opposite directions.

11. A heat exchanger according to any one of the preceding claims, wherein an exhaust pipe fitted with a venturi nozzle and having control openings arranged on the circumference upstream and downstream of the venturi nozzle is arranged within or coaxially with respect to a control pipe, the control pipe having cooling-chamber openings on the circumference in the region of the control openings of the exhaust pipe, and both pipes being arranged in such a way that they can move axially relative to one another owing to the thermal expansion.

12. A heat exchanger according to any one of the preceding claims, wherein the material of the exhaust pipe has a different coefficient of thermal expansion ftom the material of the cooling chamber or of the control pipe or the control opening is closed by a closure device made from bimetallic material.

13.. A heat exchanger for exhaust gas of an internal combustion engine, substantially as described herein with reference to and as illustrated in the accompanying drawings.